CHAPTER 3: REINFORCING WALL STRUCTURE
3.1 Construction
A single reinforcing wall on the north face of the structure was used as the first form of lateral reinforcement. The reinforcing wall was constructed of a lauan based plywood that can be purchased from most lumber or hardware stores, such as Home Depot. The wood consisted of three layers and was nominally 0.2 inch thick. The wood was originally purchased in a four foot by eight foot sheet, which had to be cut into a sheet of dimensions five foot by four foot in order to fit the structure.
After the wood was cut into a sheet of desired size, notches had to be cut out at six separate locations on the reinforcing wall. This was done in order to ensure a tight, secure fit of the reinforcing wall onto the face of the columns and around the beams. Attaching the wood directly to the face of the columns, instead of solely attaching it to the face of the beams, created a more realistic model of an actual reinforcing wall. The wall was then put in
49
place by bringing it through the top of the structure and inside the enclosed structure. This was done so that the wall could be connected to the face of both the columns and beams.
Machine bolts of a nominal diameter of 0.25 inch were used to secure the wall onto the north face of the structure. A washer was used on the outer and inner face of the wall through which the bolt was threaded. A single nut was tightened until slight crushing of the wood occurred. This proved to ensure a tight and consistent connection without harming the reinforcing wall’s integrity.
The wall was secured to the structure at five different locations of each of the two north face columns. Three connections were created in the first story on each column at two inches above the bottom beam, in the middle of the bottom and middle beam, and two inches below the middle beam. Two bolts were placed in the second story in each column at two inches above the middle beam and two inches below the top beam. One bolt, along with the two washers and one nut, was placed in the middle of each beam. This resulted in a total of thirteen connections of the reinforcing wall onto the face of the structure. The final
reinforcing wall structure is shown in Figure 3.2.
The sensors used to measure the acceleration of the structure were previously attached to the structure by magnets. Since the north face columns were covered by the reinforcing wall, the sensors had to be placed on the back of the columns, as shown in Figure 3.2. This resulted in a -x, -y, and +z sensor orientation, again making the plus/minus
orientation toggle switches in the LabVIEW program of good use.
50
Figure 3.1 – R1. Left: North face reinforcing wall as viewed from the northwest corner of the structure. Right: Back of the north face reinforcing wall as viewed from the east face.
Figure 3.2 – Left: North face reinforcing wall fashioned flat against the face of the north face columns. Right: Accelerometer oriented on the back of the north face columns.
N
51
For another configuration, a second reinforcing wall in addition to the first
reinforcing wall was added to the west face of the structure. This resulted in lateral bracing in each planar direction of the structure. The west face reinforcing wall was fashioned to the structure in a similar way as the north face reinforcing wall, with notches cut out of the wall to ensure a tight connection, five connections on each column, and a connection on each beam. However, since the structure was constructed in a way that the punched slots of the columns faced north and south, five holes had to be drilled into each column. This was done first with an electric drill and a drill bit. The hole was drilled out to a smaller diameter than the screw diameter. This removed a small amount of material from the columns. The wall was then put in place by bringing it through the top of the structure and inside the enclosed structure. This was done so that the wall could be connected to the face of the columns as well as the beams. Then, self tapping screws of inner diameter 0.15 inch and outer diameter 0.2 inch were used to secure the wall to the west face columns of the structure. An additional notch had to be cut out of the southwest corner of the reinforcing wall since this was where the structure was being excited by the impact hammer.
The locations of connections were very similar to the connections of the north face reinforcing wall. However, the west face column connections were positioned in a different way in order to ensure there was no conflicting overlapping of north and west face screws.
Again, three connections on each column were placed in the first story at one inch above the bottom beam, approximately between the bottom and middle beam, and one inch below the middle beam. Two screws were again placed in each column in the second story at one inch above the middle beam and one inch below the top beam. A washer was used on the outer face of the wall for the column connections. No washer or nut was used on the inner face of
52
the columns since the screw were self-tapping. The same machine bolt and washer configuration used on the three north face beam connections were used on the west face beam connections.
Figure 3.3 – R2. Left: North and west face reinforcing walls as viewed from the northwest corner. Right: The southeast corner of the structure.
N
y
53
Figure 3.4 – West face reinforcing wall with notch so that the structure could be excited on the origin column.